Allow Users to define custom, toggleable Layers in Maps both as overlays or as different basemaps.
This would make Kagi Maps more versatile and able to adapt to different user's needs.
A user opens a page to add custom map layers to Kagi Maps.
There they get both a list of already added maps/layers as well as the option to add new ones.
If they choose to add a new one they need to enter a name, have a toggle whether what they want to add is a vector map or tileset, an input for the new map's source (ex. "https://a.tiles.openrailwaymap.org/standard/{z}/{x}/{y}.png" for OpenRailwayMap tiles; see these for a choice of custom vector tile or raster tile providers) as well as a toggle of whether to use the map as an overlay or a basemap.
Inside Kagi Maps the custom Maps would be added to the already existing selection for basemaps as well as a new one for map layers. This helps a user customize and extend their Maps experience.
An example for software that can do this would be UMap, the raster tiles version of OpenRailwayMap where the railway part is just a simple transparent layer or the vector version of OpenRailwayMap which has a nicer UI for choosing the basemap imo.
